Most IT departments in today's corporate world face growing user demands and shrinking budgets. Thus, storage vendors desire to develop cost efficient low-end systems with value-added features and availability levels typically found usually in enterprise class facilities. An example of such systems may be a serial attached SCSI (SAS) cluster system.
SAS was developed as the evolutionary replacement for parallel SCSI (SCSI capable of supporting Serial ATA). SAS was envisioned to become the universal interconnect technology for mid-range and enterprise storage systems supporting multiple applications and deployment models and negating the need for multiple incompatible storage infrastructures. SAS provides high-end enterprise features (such as Fibre Channel or the like), as well as the ability to support low-end desktop type storage media devices (such as Serial ATA or the like).
A cluster connects two or more servers together so that they appear as a single computer to clients. Connecting servers in a cluster allows for workload sharing, enables a single point of operation/management, and provides a path for scaling to meet increased demand. Thus, clustering provides the ability to produce high availability applications. In FIG. 1, an illustration of a block diagram 100 of an exemplary SCSI cluster is shown. In the exemplary SCSI cluster, Node1 and Node2 are connected to share disks through different controllers connected to each node. The controllers are capable of communicating through a shared SCSI bus. This communication is often called Peer-To-Peer Communication (P2P). Thus, in a SCSI cluster environment, even if one node fails, a communication to the shared resources may be available through the shared SCSI bus.
However, a SAS cluster does not comprise such a shared bus suitable for P2P communication. Instead, one to one serial buses are utilized. In FIG. 2, an illustration of a block diagram 200 of an exemplary SAS cluster is shown. Node1 may access enclosure 206 through enclosure 202 and enclosure 204. However, a conventional SAS cluster does not support P2P communication between nodes if an enclosure in a SAS cluster fails. Hence controller may not be able to access other disks serially connected through the failed enclosure.
Referring now to FIG. 3, an illustration of a block diagram 300 of a SAS cluster with a failed enclosure is shown. In FIG. 3, when enclosure 304 fails, Node1 cannot access drives in enclosure 306 since the only I/O path (serial SCSI path) from Node1 to enclosure 306 is coupled to enclosure 304. Similarly, Node2 cannot access drives in enclosure 302. In the exemplary SAS cluster, Node1 cannot communicate with Node 2 once a normal I/O bus (Serial SCSI bus) is not available.
Therefore, it would be desirable to provide an alternative communication path in a SAS cluster so that a node may communicate with another node via a network when the node has lost its accessibility to shared drives. It would be also desirable to provide a system and method for supporting P2P calls which is suitable for being used through the alternative communication path in a SAS cluster.